I have read about chords lately and I'm kinda sick of chord construction because that's all what is out there.
I have source on chord progressions also.

What I'm searching for is a source on how to use more complex chords (7th, 6th, add9,11,13 and their alternatives, flattened, sharpened and so on).
For now only trial and error helps me but that I just can't see the light. There must be some system to it, at least a basic one.

Anyone knows a source on this?
Apart from the basics of diatonic harmony and consonance/dissonance, there isn't a formula or anything.

If it sounds good, it is good
Ok Theory books are great,
but the rule of thumb is if you use complicated chords
the more notes in common two chords have the smoother the transition
thats why I to IV or V will go really smoothly, the same is true with suspended chords and
9ths 7th or whatever, the more notes in common the smoother the transition
and the more dissonance the more it wants to be followed by consonance
as long as that's what you want, you make it more jarring by using the opposite approach
and keep in mind you can use complicated chords to change key, If they belong to another key as well as the one you're in you can change key in the middle of a chord progression without anyone noticing, and just make a cool sound.
chord chemestry by ted greene might be helpful....he has some great chord arrangements and ananysis of songs and blues progressions...and a chord reference with all the chords you are looking for....check his web site also....

play well

Thank you for your advices.

Thanks wolflen, I'm going to check that book.
Yeah as someone above said, it's about the common notes in the extended chords. Whether they be common to the melody and help accentuate certain notes, or if the give you a preview and an extra smooth transition to the next chord, or if they are half one chord chord and haf of the next and you stick it in for a smoother transition.